THEORY OF THE GEOMAGNETIC DYNAMO BASED ON MEAN FIELD ELECTRODYNAMICS

A survey is given on the present state of the geomagnetic dynamo theory which is based on the electrodynamics of mean fields in electrically conducting turbulent media. Models of both the α2-type and the αω-type are taken into consideration, i.e. models where the α-effect alone, or together with a differential rotation, gives rise to the regeneration of magnetic fields. Results of special investigations are given and discussed. Models of the α2-type apply to the Earth provided that it shows no noticeable differential rotation. It is pointed out that such models can explain not only the generation of a magnetic field with an axisymmetric dipole-like structure, but also the occurrence of non-axisymmetric components and their westward drift. If, however, a noticeable differential rotation exists, models of the αω-type have to be envisaged. Such models also allow an understanding of the existence of a magnetic field with an axisymmetric dipole-like structure, but they do not provide for a straightforward interpretation of the occurrence and behaviour of the non-axisymmetric components. © 1979.